This invention relates to semiconductor detectors, and more particularly to the improvement of the electrical and mechanical integrity of such detectors connected to external structures or electronics.
In a conventional flip-chip 100 shown in FIG. 1, a semiconductor chip or die can have bumped terminations spaced around an active area of the die. The terminations are intended for face-to-face attachment of the semiconductor die to a substrate 102 or another semiconductor die. The bumped terminations of the flip-chip 100 often include an array of minute solder balls or epoxy bonds 104 disposed on a front attachment surface of a semiconductor die. The attachment of a flip-chip 100 to a substrate 102 or another semiconductor involves aligning the epoxy bonds 104 on the flip-chip 100 with a plurality of contact points 106 on a facing surface 108 of the substrate 102. The contact points 106 are configured to be a mirror image of the epoxy bond arrangement 104 on the flip-chip 100. A plurality of epoxy bonds 104 may also be formed on the facing surface of the substrate 102 at the contact points 106. In some applications, semiconductor illumination detector chips are attached to structures such as printed circuit boards (PCBs) or signal processing electronics in a flip-chip interconnection.
Several techniques exist for forming flip-chip interconnections between semiconductor photodetectors and external structures. These include solder bump interconnection, silver epoxy bonding, and indium bump bonding. The silver epoxy bonding is a relatively simple technique that has been widely used for flip-chip bonding of semiconductor photodetectors to external structures. The silver epoxy is silver-filled epoxy having a suspension of silver particles in an epoxy paste. The paste, mixed with a compatible hardening agent, is applied in liquid form to the contacts on the photodetector and/or the external structures. The front surfaces of the chip and external structure are aligned mechanically. The surfaces are then brought into sufficiently close proximity so that the silver epoxy forms a bridge between the mating contacts on the two components. However, the liquid nature of the epoxy itself imposes limits on the minimum spacing between adjacent contacts that can be bonded. An appropriate curing cycle causes the silver epoxy to cure into conductive, rigid or semi-rigid, interconnections between the two components.
Since the metal electrical contacts on a photodetector often resides directly on the surface of the semiconductor material itself, any migration of the components of the silver epoxy through the metal contact can cause degradation of the electrical properties of photodetector structures. Further, an exposure of the flip-chip photodetector to repeated cycles between low and high temperatures may cause failure of the electrical and mechanical connection. Such failures are often caused by mechanical stresses to the assembly resulting from the difference between the coefficients of thermal expansion (CTE) of the semiconductor material and the external structure. Forces applied to the assembly by other means may also cause failure of the interconnection. In some cases, the stresses on the metal-to-semiconductor interface are sufficient to pull a portion of the semiconductor material away from the surface of the chip.
The present disclosure includes a semiconductor interconnection device having a semiconductor die, a plurality of epoxy bonds, and an array of insulating islands. The semiconductor die has a plurality of conductive contacts. The plurality of epoxy bonds contains a metallic component such as silver. The epoxy bonds are configured to provide interconnection between the semiconductor die and an external structure. The plurality of epoxy bonds is selectively applied to the plurality of conductive contacts on the semiconductor die and corresponding conductive contacts on the external structure. The array of insulating islands is coupled to the plurality of conductive contacts. The islands are configured to prevent migration of the metallic substance from the plurality of epoxy bonds to the semiconductor die through the plurality of conductive contacts.
The present disclosure also includes a method of manufacturing a flip-chip interconnection device. The method includes providing an array of insulating islands on a semiconductor die, applying a plurality of metal contacts over the array of insulating islands, and selectively depositing an array of epoxy bonds on the plurality of metal contacts. The array of insulating islands prevents migration of metallic component in the array of epoxy bonds into the semiconductor die.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.